1. Field of the Invention
This invention relates to an image pick-up apparatus, e.g., a color television camera apparatus of a structure such that an image pick-up unit for picking up an image of an object and a signal processing unit for implementing a signal processing to image pick-up outputs of three primary colors from the image pick-up unit can be separate through a transmission unit, and more particularly to an image pick-up apparatus adapted to correct phase differences produced between respective image pick-up outputs when transmitted from the image pick-up unit to the signal processing unit.
2. Description of the Related Art
Generally, in image pick-up apparatuses such as color television camera apparatuses for business use for which high picture quality and high resolution are required, an image pick-up light of an object is color-separated into rays of light in the wavelength region of three primary colors of red (R), green (G) and blue (B) by means of a prism, etc. to pick up images of these rays of image pick-up light of three primary colors by using different image pick-up tubes or image pick-up devices, respectively, thus to form image pick-up outputs of three primary colors. Then, these image pick-up outputs of three primary colors are synthesized by the signal processing to form an output video signal.
In image pick-up apparatuses adapted to color-separate an image pick-up light into three primary colors to respectively pick-up their images in a manner stated above, it is required, in forming an output video signal, to allow phases of respective image pick-up outputs to be in correspondence with each other so that respective pictorial images of three primary colors precisely overlap with each other.
For this reason, in image pick-up apparatuses using e.g., image pick-up tubes, an approach is employed to adjust registration in regard to centering of R, G and B images, etc. by varying the deflection characteristics of respective image pick-up tubes, or the like to thereby correct phase differences between image pick-up outputs of three primary colors at the time of start of photographing.
Further, in image pick-up apparatuses using solid state image pick-up devices such as CCD (Charge Coupled Devices), etc., since phases of respective image pick-up outputs are determined in dependency upon positions of respective image pick-up devices, if an approach is employed at the time of manufacturing to adjust the above-mentioned centering to fix the respective image pick-up devices, an adjustments by user could become unnecessary. In addition, for example, as proposed in the Japanese Patent Application Laid Open No. 146589/85, there is known a technique to electrically correct phase differences between image pick-up outputs from the solid state image pick-up devices.
Meanwhile, in recent years, in image pick-up apparatuses of this kind, there have been developed apparatuses of a structure such that the image pick-up unit for picking up an image of an object and the signal processing unit for implementing a signal processing to image pick-up signals are separate and independent to transmit image pick-up outputs of three primary colors formed in the image pick-up unit to the signal processing unit through transmission paths such as coaxial cables or optical fiber cables, etc, respectively. For example, image pick-up apparatuses of such a structure are used for apparatuses in which the image pick-up unit is extremely miniaturized so that a special photographing can be carried out, apparatuses for high definition television such as high vision, etc. and provided with a very large signal processing unit.
However, when an attempt is made to transmit image pick-up outputs of three primary colors formed at the image pick-up unit in a manner stated above through transmission paths different from each other, respectively, there may occur differences between delay times in transmitting respective video outputs resulting from the difference between characteristics such as wavelength shortening rate or refractive index, etc. of respective cores constituting these transmission paths, or differences between length of respective cores in cabling, etc.
For this reason, even if phases of respective image pick-up outputs transmitted through transmission paths different from each other are in correspondence with each other between respective image pick-up outputs when outputted from the image pick-up unit, any phase difference or shift may occur at the signal processing unit. In addition, quantities of phase differences may vary by changing the transmission paths.
Accordingly, in the apparatuses of a structure to respectively transmit image pick-up outputs of three primary colors through transmission paths of the above-mentioned apparatuses using solid state image pick-up devices, it is required to correct phase differences produced between image pick-up outputs resulting from differences between lengths of transmission paths.
Particularly, in apparatuses for high definition television, since resolution or picture quality is extremely degraded when any color shift occurs, it is required to rigorously correct such phase difference.